1. Field of the Invention
The present invention relates to devices for use in cleaning laundry or dishes, and more particularly to a dispensing device and method for dispensing substances, such as chemicals, in water for use in the cleaning or treatment of laundry.
2. Description of the Background Art
Laundering of clothes and other fabrics to remove soil and other common contaminants is well known in the art, and is a part of daily living in many parts of the world. Prior to the mid twentieth century home laundering was a laborious task, usually consuming an entire day of work. Since World War II, however, great strides have been made in the convenience of home washing. The automatic washer and dryer revolutionized the chore of home laundering. Consequently, heating water to fill the washer, using the washer and wringer, and hanging linen and clothing to dry have become obsolete with the home laundering equipment now available. By merely loading clothes in a washing machine and adding detergent, the modern home machine automatically puts the clothes through a suds cycle and one or two rinse cycles. Thus, a person is freed to do other things while the wash is being done, and, instead of hanging the clothes to dry, a person can now remove them from the washer and quickly dry them in a dryer.
In the middle ages, soap was made at home and used for cleaning laundry. Cake soap, however, was a luxury product that came into common use only in the 19th century. The synthetic relatives of soap, detergents were developed during World War II when the natural ingredients for soap became scarce. Unlike soap, detergents are synthetics and do not form easily biodegradable waste products.
By the 1950's detergents had become more popular than soap for general laundering and dish washing since soap, when used in hard water (i.e. water that contains a large amount of dissolved mineral salts), reacts, unlike detergents, with the dissolved salts to form a whitish gray precipitate responsible for the common bathtub ring.
Sodium sulfonates make up the most common group of detergents. Sodium alkylbenzene sulfonate, or sodium ABS, was one of the earliest detergents. Its molecules comprise a long chain of hydrocarbons formed by linked carbon atoms having two hydrogen atoms attached to each carbon atom. The chain is not straight: the carbon atoms branch off at one end. This is the hydrophobic part that attaches to soil. Attachment to the soil is facilitated by the ionic attraction between the positively charged soil particles and the negatively charged hydrophobic end of the molecule. At the other end, a sodium sulfonate molecule attaches to water.
The detergents used for washing clothing also typically include a number of additives--for example, bleaches, brighteners, and abrasives. Bleaches whiten fabrics by destroying dirt and colors. Brighteners are chemicals that convert normally invisible ultraviolet light into visible light, such that additional light reflects back from the fabric, making it seem more vivid, or "whiter." Abrasives are ground-up particles of sand or other rock minerals added to detergents to scour stains.
The basic cleaning agents in detergents are called surface-active agents, or surfactants. When added to liquid, they reduce the liquids surface tension (the affinity that the liquid's surface molecules have for each other), thereby increasing the liquid's spreading and wetting properties. Part of the surface-active molecule is hydrophilic, or "water loving," and another part is hydrophobic, or water-repellant.
The seemingly simple action of cleaning a soiled surface is actually a complex four-step process. First, the surface to be cleaned is made wet. Soaps and detergents help the water spread out and wet the surface by penetrating the fabric fibers. Second, the surface absorbs the soap or detergent. The hydrophilic part of the surface-active molecule attaches itself to the water, and the hydrophobic part attaches itself to the solid or fiber, and most important, to the soil. In the third step, the soil is broken up into small beads that can be washed away. Mechanical agitation helps the surface-active molecules pull the dirt away from the material and into the water. Finally, the dirt is rinsed away in the water.
Furthermore, the acidity or pH level of laundry water has been found to enhance detergent cleaning effectiveness. An acid is a compound containing hydrogen which releases hydrogen ions (H+) in an aqueous solution. This causes the hydrogen atoms to become electrically charged ions with a strong tendency to react with other substances, hence, the corrosiveness of many acids. The acidity of a solution is thus based on the hydrogen ion concentration and is commonly referenced in terms of the solution's pH level. A neutral solution has a pH level of 7.0, while an acidic solution has a pH level below 7.0, and an alkaline or basic solution has a pH level higher than 7.0.
By adjusting the pH level of laundry water, it has been found that cleaning effectiveness can be greatly enhanced. Specifically, many commercial and industrial laundry cleaning systems utilize high pH laundry water solutions to improve cleaning performance. While high pH laundry water improves cleaning performance, it can also result in fabric discoloration and reduction in fabric tensile strength.
Accordingly, many commercial and industrial laundry processes utilize a two step process wherein the pH level of the laundry water is first raised to improve cleaning effectiveness, then reduced, or neutralized, to prevent discoloration and tensile strength reduction. The two step process is accomplished, either manually or automatically, by the addition of effective amounts of pH altering chemicals at predetermined periods. Thus, in addition to detergent formulations, an effective amount of very alkaline (e.g. high pH) ingredients are added, at high wash water temperatures (e.g. 160.degree. -180.degree. F.). Examples of such alkaline ingredients include soda ash, silicates and various other caustic ingredients in addition to various phosphate blends. In the second step of the process, acidic blends, known as "laundry sours" are added to reduce the alkaline pH of the wash water for preventing fabric discoloration and tensile strength reduction. Examples of such laundry sour ingredients include sodium silico-fluorides and sodium biflourides.
This process, however, is not practical in non-commercial, household laundry cleaning applications since consumers are generally not willing to attend to the addition of multiple chemical compositions at various time intervals during a single wash cycle requiring the consumer to constantly monitor the wash cycle. Thus, commercially available laundry detergents marketed and sold for home use comprise pH neutral detergent solutions. Accordingly, the cleaning effectiveness of commercially available home laundry detergents is not fully realized. Thus, there exists a need for an apparatus and method for varying the pH level of laundry water in a predetermined manner without requiring the user to repeatedly add chemicals during the washing process.